1. Field of the Invention
The present invention relates to a printing apparatus and a control method therefor and, particularly, to a printing apparatus including an inkjet printhead and an inkjet printhead control method used in the apparatus.
2. Description of the Related Art
Among printing apparatuses which are used as printing means for images, characters, and the like in a printer, copying machine, or facsimile apparatus, inkjet printing apparatuses (to be simply referred to as printing apparatuses hereinafter) perform printing by discharging ink from an inkjet printhead (to be simply referred to as a printhead hereinafter) onto a printing medium.
The printing apparatuses are roughly classified into a serial type printing apparatus which performs printing while scanning the printhead in a direction intersecting the conveyance direction of the printing medium, and a line type printing apparatus which performs printing while holding, at a fixed position, a full-line printhead having a print length corresponding to the full width of the printing medium.
The above-described serial type printing apparatus generally sets a printing medium at a predetermined position, and repeats reciprocal movement of a carriage, in a predetermined direction on the printing medium, to which the printhead is mounted and paper conveyance by a predetermined amount, thereby printing images on the entire surface of the printing medium.
A printing apparatus which supports color printing and has an arrangement including a plurality of printheads each corresponding to one ink color has become widespread. To realize recent high photo quality printing, the size of droplets discharged from the printhead has become small. To discharge such small droplets, the diameter of each nozzle of the printhead has also become small. A general printhead has nozzles with a diameter of about 10 to 50 μm.
Some printing apparatuses adopt an arrangement in which an ink tank and printhead are separable/exchangeable. For this type of printing apparatus, an ink channel between an ink tank and a printhead is temporarily exposed in exchanging the ink tank, and thus a foreign substance such as dust may enter the ink channel. If a foreign substance enters the ink channel, and reaches a nozzle, clogging of the nozzle may occur depending on the size of the dust, thereby causing an ink discharge failure.
To solve this problem, for example, as disclosed in Japanese Patent Laid-Open No. 2-198861, a filter for preventing a foreign substance from entering a portion where ink is supplied has been conventionally provided.
In the above conventional example, however, if an ink tank is detached from a printhead, the filter including ink is undesirably exposed to the outer air. If the filter is left in that state for a long time, the viscosity of ink increases due to evaporation of volatile components, and clogging of the filter may occur. If clogging of the filter occurs, ink may not be smoothly supplied to the printhead, thereby causing an ink discharge failure.